This invention relates to the field of calibrating microphones or pressure transducers or similar apparatus.
In the calibration of devices which are commonly called microphones and involve acoustic signal pressures in the range of one pound per square inch and lower values, and also in the calibration of pressure to electrical transducer elements, involving input pressures above one pound per square inch, it has been common practice to employ sinusoidal excitation of the device being calibrated, with the frequency of the sinusoid being altered either manually or automatically. Although calibrations performed in this manner may be made as accurate as desired and usually involves a minimum of complex theory and calculations, the time and apparatus required in performing such calibration can detract from their practical utility especially in the field or in other non laboratory situations.
Nevertheless there is found to be an ongoing and, in fact, increasing need for a calibration arrangement which can be accomplished quickly and with reasonable accuracy. It is especially desirable that a usefuL calibration arrangement avoid the tedium and expense of point by point sinusoidal comparisons while also providing a capability for use with a variety of transducer amplitude and frequency response ranges. It is also desirable for the calibration arrangement to accomodate microphones and pressure transducers (hereinafter transducer under test devices) which are of a variety of physical sizes including the miniature devices frequently mounted on or near the moving element of an apparatus.
In addition to sinusoidal calibration apparatus, the prior art calibration devices include such arrangements as a motor driven piston exciter and an impulse apparatus of the type wherein a diaphram covering a reservoir of compressed gaseous fluid is suddenly ruptured and other valving arrangements wherein a test chamber is exposed to a region of differential fluid pressure.
The prior patent art sinusoid and sinusoid-like calibration apparatus include U.S. Pat. Nos. 3,224,246; 3,281,543; 3,548,631; 3,659,255; and 3,744,294. In addition, the patent art also includes the patent of A. R. Zias et al, U.S. Pat. No. 4,051,712 which describes a pressure reference signal generator capable of establishing known reference input pressures for a transducer device in order to accomplish an automatic calibration sequence. The Zias et al apparatus is, however, especially concerned with providing long duration signals capable of calibrating the offset characteristics of a transducer.